/*
 *  ReadOnlyTransaction.java        22-ott-2009
 *   
 * Copyright (c) 2009 mentalsmash.org
 *  
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 * 
 *  http://www.apache.org/licenses/LICENSE-2.0
 * 
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 * 
 *  The use of the Apache License does not indicate that this project is
 *  affiliated with the Apache Software Foundation.
 */

package org.mentalsmash.tazio.transactions.management;

import java.util.Set;

import org.mentalsmash.documentation.Concurrency;
import org.mentalsmash.tazio.commons.identifiers.OID;
import org.mentalsmash.tazio.transactions.identifiers.TID;
import org.mentalsmash.tazio.transactions.objects.Snapshooter;

import com.google.inject.Inject;

/**
 * Concrete implementation of {@link TazioTransactionImpl} for
 * ReadOnlyTransactions.
 * <p>
 * Theoretically a read only transaction could always succeed, but this would
 * require a quite more complicate interaction protocol between Replicas. <br />
 * Therefore for now the only purpose for this class - besides being a
 * placeholder - is to check that no writes are performed during the access to
 * objects
 * </p>
 * 
 * @author Andrea Reale
 * @version 0.0.1
 */
@Concurrency(concurrentAccess = true, // a transaction may only be access by the
// thread that owns it
// or by a thread the commits it.
specification = "no non-final status variable. No concurrency concerns.")
final class ReadOnlyTransaction extends TazioTransactionImpl {

    /**
     * @param tm
     * @param snapshooter
     * @param tid
     */
    @Inject
    public ReadOnlyTransaction(final SystemTransactionManager tm,
	    final Snapshooter snapshooter, final TID tid) {
	super(tm, snapshooter, tid);
	// TODO Auto-generated constructor stub
    }

    private static final long serialVersionUID = 5093253668871177708L;

    /**
     * Throws a ReadeOnlyAccessException if invoked
     * 
     * @throws ReadOnlyAccessException
     *             every time
     * @return does not return anything, it throws an exception, as I said
     */
    @Override
    public Set<OID> getWriteSet() {
	throw new ReadOnlyAccessException(
		"Read only transactions do not have write sets!");
    }

    /**
     * Throws a ReadeOnlyAccessException if invoked
     * 
     * @throws ReadOnlyAccessException
     *             every time
     */
    @Override
    public void addToWriteSet(final OID id) {
	throw new ReadOnlyAccessException(
		"Read only transactions do not have write sets!");
    }

}
